1 files changed, 72 insertions, 0 deletions
diff --git a/vendor/gix-hashtable/src/lib.rs b/vendor/gix-hashtable/src/lib.rs
new file mode 100644
index 000000000..6392a9a5c
--- /dev/null
+++ b/vendor/gix-hashtable/src/lib.rs
@@ -0,0 +1,72 @@
+//! Customized HashMap and Hasher implementation optimized for using `ObjectId`s as keys.
+//!
+//! The crate mirrors `std::collections` in layout for familiarity.
+#![deny(missing_docs, rust_2018_idioms)]
+#![forbid(unsafe_code)]
+
+use gix_hash::ObjectId;
+pub use hashbrown::{hash_map, hash_set, raw, Equivalent};
+
+/// thread-safe types
+pub mod sync {
+    /// A map for associating data with object ids in a thread-safe fashion. It should scale well up to 256 threads.
+    pub struct ObjectIdMap<V> {
+        /// Sharing is done by the first byte of the incoming object id.
+        shards: [parking_lot::Mutex<super::HashMap<gix_hash::ObjectId, V>>; 256],
+    }
+
+    impl<V> Default for ObjectIdMap<V> {
+        fn default() -> Self {
+            Self {
+                shards: std::array::from_fn(|_| parking_lot::Mutex::new(super::HashMap::default())),
+            }
+        }
+    }
+
+    /// access and modifications - we only implement what's used within the `gix-*` ecosystem.
+    impl<V> ObjectIdMap<V> {
+        /// Insert `value` at `key` and return `None` if it's the first value at that location, or `Some(previous-value)`
+        /// if `key` was already set.
+        pub fn insert(&self, key: gix_hash::ObjectId, value: V) -> Option<V> {
+            self.shards[key.as_slice()[0] as usize].lock().insert(key, value)
+        }
+    }
+}
+
+///
+pub mod hash {
+    /// A Hasher for usage with HashMap keys that are already robust hashes (like an `ObjectId`).
+    /// The first `8` bytes of the hash are used as the `HashMap` hash
+    #[derive(Default, Clone, Copy)]
+    pub struct Hasher(u64);
+
+    impl std::hash::Hasher for Hasher {
+        fn finish(&self) -> u64 {
+            self.0
+        }
+
+        #[inline(always)]
+        fn write(&mut self, bytes: &[u8]) {
+            self.0 = u64::from_ne_bytes(bytes[..8].try_into().unwrap());
+        }
+    }
+
+    /// A Hasher for usage with HashMap keys that are already robust hashes (like an `ObjectId`).
+    /// The first `8` bytes of the hash are used as the `HashMap` hash
+    #[derive(Default, Clone, Copy)]
+    pub struct Builder;
+    impl std::hash::BuildHasher for Builder {
+        type Hasher = Hasher;
+
+        fn build_hasher(&self) -> Self::Hasher {
+            Hasher::default()
+        }
+    }
+}
+
+/// A HashMap for usage with keys that are already robust hashes (like an `ObjectId`).
+/// The first `8` bytes of the hash are used as the `HashMap` hash
+pub type HashMap<K, V> = hashbrown::HashMap<K, V, hash::Builder>;
+/// A HashSet for usage with keys that are already robust hashes (like an `ObjectId`).
+/// The first `8` bytes of the hash are used as the `HashMap` hash
+pub type HashSet<T = ObjectId> = hashbrown::HashSet<T, hash::Builder>;